Drill string jars, or drilling jars, are installed as part of the drill string in a well and commonly serve as a length of the drill string. At least one jar is commonly placed above that portion of the drill string most likely to get stuck in the well. When the drill string gets stuck below the jar, axial load is applied to the jar in preparation for jarring the stuck portion. The axial load may be in tension or compression if the jar will accept both. The latch is then released (or actuated) to allow the jar to telescope to change length. The length change between the stuck portion of the drill string and the free, and stressed, portion of the drill string imparts a velocity to a rather heavy mass of the drill string. When the telescoping movement runs out, it is stopped suddenly, jarring the stuck portion.
Latches for drilling jars have taken many forms. Some actuate by axial stress in excess of that needed for drilling. Some are released by excess axial stress and another factor such as torque or drilling fluid pressure. Apparatus of this invention is actuated by excess axial stress only. This invention pertains to the latch only and descriptive matter pertaining to details of construction of telescoping jars is for clarity of the latch description.
There are many latches for telescoping jars in the art. Some have provisions for rigsite adjustment of the axial force required for latch release. Complexity of any drill string component is an undesirable factor. Simplicity is always a desired design objective.
Some drill string jars are installed in a particular location in the drill string relative to the drill head and the adjustment is never changed between the jars shop overhaul sequences. Such jars invite simplicity of construction. It is therefore an object of this invention to provide a drilling jar latch of simple design and construction. It is a further object of this invention to provide a drilling jar latch that can be adjusted during assembly by selection of low cost components with dimension choices determining the release forces. It is another object of this invention to provide a drilling jar latch that can be used in tension or compression with the release forces for each independently adjustable by dimension choices of components used in assembly.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.